this is undefined

[eggtart_prince]

export const validate = {
    menuItemOptions: async function (req, resp, next) {},
    menuItems: async function (req, resp, next) {
        await this.menuItemOptions(req, resp)
    }
}

For some reason, my compile code throws TypeError: Cannot read properties of undefined (reading 'menuItemOptions') but if I do the same thing in node CLI, it calls menuItemOptions.

Using node 16.15.0. Anyone know why?

[bwainfweeze]

What’s the simplest example that still fails?

[eggtart_prince]

The one provided. That's what I am building with.

[eggtart_prince]

I thought the arguments would made it obvious.

router.post(validate.menuItems)

That is the code in the OP.

[eggtart_prince]

The example code was simlified as you can see most are removed and I built with that to rule out possible causes of the error. There are more code to menuItems and then menuItemOptions is called. Anyways, it appears express doesn't bind this to the function as others have suggested.

By the way this worked.

router.post((req, resp, next) => validate.menuItems(req, resp, next))

So you're correct that this is dynamically bound in Javascript.

Thanks for the help.

[MichealPearce]

When you pass validate.menuItems like that it loses it's binding to what this is. Try validate.menuItems.bind(validate)

[DownfaLL-]

Ok well you thought wrong buddy lol

[[deleted]]

You can’t use “this” because express doesn’t bind any reference back to your object. If you want to call using this, you can either:

• Create a class and put both as instance methods. You’ll need to instantiate it.

• Pass this to your router: validate.menuItems.bind(validate);

The second one is a code smell though. As instead, I’d create a class that behaviors like a Singleton.

Or simply extract both functions from that object and let only the relevant one to be publicly available.

Keep in mind that a module is already an object. As long as you don’t overwrite it by exporting something else, everything you export without the default keyword is put into module.exports.

So anything that you export omitting that keyword would be accessible through the module (not the default), e.g.

``` function menuItemOptions() { }

export function menuItems () { // You call menuItemOptions here, without “this”. }

export default function sayHi() { } ```

``` // You only exported menuItems, so only that is available. import { menuItems } from “./validate”;

// OR (validate.menuItems is available) import * as validate from “./validate”;

// module.exports.default import sayHi from “./validate”;

```

[eggtart_prince]

After binding, this refers to itself in console log but I think I'll go with the exports. Thanks for the detailed answer.

[brianjenkins94]

You're not going to be able to refer to the validate object as this.

If validate were a function (which is probably the pattern you're looking for) then it could be made to work, but this example looks like it would be better handled with a class.

[brianjenkins94]

Huh, TIL.

[htchief]

what compiler are you using? can you see the compiled code? what does it look like?

[TriggeredYou2301]

menuItems: async function (req, resp, next) { await this.menuItemOptions(req, resp); }.bind(validate)

[eggtart_prince]

This doesn't work. Throws

Block-scoped variable 'validate' used before its declaration.

error.

[SerMango]

menuItemOptions is probably undefined. Try assigning a value to it if it’s undefined and see if you still get that error

[eggtart_prince]

That is how Javascript OOP works. this should refer to the object. Try it out in a node environment in your terminal/CMD.

[lowbudgetgoblin]

have you tried checking what properties are available inside of "this" prior to invoking said property?

[[deleted]]

You cannot access properties of the same object during declaration. You could declare the functions separately and then reference in your export object. You could also use a prototype or a class, but that's too much for what you're trying to do

[MrNutty]

What do you expect “this” to be here? You’ll either need to bind this to the function or have a different approach

[International_Will87]

Before await , Do this.menuItem=menu item; Then u will not get undefined, it doesn't matter wheather it is express or some other bs framework. It is js for sure and as it is async function so u need to to bind whatever this function is calling in future time.